1. Field of the Invention
The present invention relates to the technical field of collimating plates for collimating diffused light and of backlighting devices, particularly to a light collimating system and a collimated light source for backlighting a liquid crystal display.
2. Description of Related Art
Liquid crystal displays (LCDs) have increasingly replaced cathode ray tubes as display devices for computers, their main advantages being small thickness, low weight and low energy consumption. For many applications, e.g. medical diagnosis and space technology, it is desirable to have images of high contrast displayed at a large range of viewing angles. While original designs were unsatisfactory in this respect, more recent designs of LCDs provide a backlighting system generating collimated light which, having passed through an LCD panel, is dispersed by a diffusing plate, offering an improved range of viewing angles.
Several designs of collimated light sources have been made, as shown in FIG. 2. U.S. Pat. No. 6,327,091 B1 teaches a plurality of light transmitting spheres 1a placed on a transparent support 2 in partial contact therewith at light transmitting areas, outside which passage of light is blocked, defining an open area ratio. Light passing from the transparent support 2 through the plurality of light transmitting spheres 1a is collimated by diffraction. A light utilization factor xcex7 is defined as the power of transmitted light over the power of incident light. An open area ratio of 0.03 results in xcex7=0.079, of 0.05 in xcex7=0.35. The open area ratio is adjusted for an optimum trade-off between transmitted intensity and collimation. An intensity halfwidth of about xc2x115xc2x0 is achieved, as compared to an intensity halfwidth of about xc2x125xc2x0 of previous devices. In another design taught in U.S. Pat. No. 5,839,812, collimation of light by diffraction is brought about by an array of cones 1b on a transparent support 2.
Collimated light sources according to U.S. Pat. Nos. 5,839,812 and 6,327,091 B1 offer only a low intensity efficiency of generated light. Furthermore, the design according to U.S. Pat. No. 5,839,812 is complicated, implying high manufacturing cost.
It is an object of the present invention to provide a light collimating system having a high yield of light intensity at a narrow angular intensity distribution.
Another object of the present invention is to provide a collimated light source which allows to maximize incident light intensity by having a reflecting light blocking area at a light incident side.
A further object of the present invention is to provide a collimated light source having a large illuminating area without requiring a light guide.
A further object of the present invention is to provide a collimated light source which admits a large variety of light sources, such as light bulbs, neon lamps, mercury-vapor lamps or cold or hot cathode ray sources, and allows for a variety of shapes of emitted light bundles for a wide range of applications.
The light collimating system of the present invention comprises a transparent substrate, a plurality of conic elements and a screen. Each of the conic elements has a relatively narrow light incident side to which the screen is attached and a relatively wide light emitting side attached to the transparent substrate. The screen has a plurality of transmission areas covered by the light incident sides of the conic elements. Outside the transmission areas, light is reflected from the screen. Diffuse light entering the conic elements through the transmission areas of the screen is collimated by refraction and total reflection at peripheral surfaces of the conic elements, resulting in a light bundle of narrow angular distribution emanating from the transparent substrate. The conic elements each have a single conic segment or a plurality of conic segments with opening angles that narrow towards the light emitting sides thereof. The shape of the conic elements ensures a high yield of light intensity at a narrow angular intensity distribution.
The present invention can be more fully understood by reference to the following description and accompanying drawings.